Protective Crown Reinforcement For Aeroplane Tire

ABSTRACT

Protective reinforcement ( 3 ) for a tire has a mean radial thickness T at least equal to two times the diameter D of a − 12 -reinforce ( 4 ), comprises respectively on its radially interior face ( 31 ) and on its radially exterior face ( 32 ) parts ( 7 ) made of elastomeric compound having an axial width W at least equal to the diameter D of a − 12 -reinforcer ( 4 ), and the path of any − 12 -reinforce ( 4 ), in the circumferential direction (XX′), varies radially between the radially interior first face ( 31 ) and the radially exterior second face ( 32 ), in such a way that the set of paths of the reinforcers ( 4 ) of the protective reinforcement ( 3 ) constitutes a three-dimensional lattice. Furthermore, the path of any − 12 -reinforce ( 4 ), in the circumferential direction (XX′), is a zigzag curve extending axially over the entire axial width L of the protective reinforcement ( 3 ).

The present invention relates to an aircraft tire and, in particular, tothe protective reinforcement of an aircraft tire.

In general, since a tire has a geometry exhibiting symmetry ofrevolution with respect to an axis of rotation, the geometry of the tireis generally described in a meridian or radial plane containing the axisof rotation of the tire. For a given meridian plane, the radial, axialand circumferential directions respectively denote the directionsperpendicular to the axis of rotation of the tire, parallel to the axisof rotation of the tire and perpendicular to the meridian plane.

In what follows, the expressions “radially”, “axially” and“circumferentially” respectively mean “in the radial direction”, “in theaxial direction” and “in the circumferential direction” of the tire. Theexpressions “radially on the inside of and, respectively, radially onthe outside of” mean “closer to and, respectively, further away from,the axis of rotation of the tire, in the radial direction, than”. Theexpressions “axially interior, and, respectively, axially exterior” mean“closer to and, respectively, further away from, the equatorial plane ofthe tire, in the axial direction, than”, the equatorial plane of thetire being the plane perpendicular to the axis of rotation of the tirepassing through the middle of the tread of the tire.

The protective reinforcement of the tire is a cylindrical structurehaving as its axis of revolution the axis of rotation of the tire. Theprotective reinforcement extends axially from a first axial end as faras a second axial end over an axial width L and extends radially from aradially interior first face as far as a radially exterior second faceover a mean radial thickness T. In the radial direction, the protectivereinforcement is a stack of at least one protective layer made up ofreinforcing elements or reinforcers that are metal or textile. Thereinforcers are coated in an elastomeric compound, namely in a materialbased on natural or synthetic rubber obtained by blending variousconstituents. When the protective reinforcement is made up of a stack ofat least two protective layers, the axial width L of the protectivereinforcement is the axial width of the protective layer of greatestaxial width, and the mean radial thickness T of the protectivereinforcement is the sum of the mean radial thicknesses of theprotective layers. The protective reinforcement is radially on theinside of a tread and radially on the outside of a workingreinforcement. The protective reinforcement essentially protects theworking reinforcement from attack likely to spread through the treadradially towards the inside of the tire.

The tread is the part of the tire that is intended to come into contactwith the ground via a radially exterior tread surface: this is thewearing part of the tire. In the case of an aircraft tire, the tread,comprising at least one elastomeric compound, is usually made up ofcircumferential ribs separated by circumferential voids known ascircumferential grooves.

The working reinforcement, radially on the inside of the protectivereinforcement, is also a cylindrical structure having as axis ofrevolution the axis of rotation of the tire. In the radial direction,the working reinforcement is a stack of at least two working layersusually made up of textile reinforcers coated in an elastomericcompound. In an aircraft tire, the reinforcers of a working layergenerally follow, in the circumferential direction of the tire, aperiodic zigzag path the amplitude of which defines the axial width ofthe working layer. The working reinforcement governs the mechanicalbehaviour of the crown of the tire. The assembly made up of the workingreinforcement and the protective reinforcement constitutes the crownreinforcement.

According to current aircraft tire designs, the protective reinforcementis often made up of a single protective layer. The protective layercomprises either metal reinforcements following a wavy path in thecircumferential direction of the tire or textile reinforcers having awavy path in the circumferential direction of the tire or making anangle with the circumferential direction of the tire.

In the case of a protective layer with metal reinforcers following awavy path in the circumferential direction of the tire, the mass of theprotective reinforcement is relatively high given the mass of the metalreinforcers, and this is penalizing in terms of the mass of the tire andtherefore of the payload carried by the aircraft.

Whether the protective layer comprises metal reinforcers following awavy path or textile reinforcers following a wavy path or lying at anangle, it has been found that the protective reinforcement can sometimesbe insufficient to prevent the migration of foreign objects from thetread to the working reinforcement, in other words that it may beinsufficiently resistant to foreign object damage (FOD). Specifically,given the harsh conditions in which it is used, these beingcharacterized by a high inflation pressure, a high static load and ahigh speed, an aircraft tire is particularly sensitive to any attack onits tread by a piercing foreign object, which may be present by chanceon the runway. In the event of such an attack on the tread, the piercingforeign object, having passed through the protective reinforcement, canprogress towards the working reinforcement. If the working reinforcementis completely pierced, this may result in a slow loss of pressure andgeneral damage to the structure of the tire. If the workingreinforcement is partially pierced, the retreadability of the tire,namely its ability to have its tread replaced after it has worn away,can no longer be guaranteed.

It is an objective of the present invention to increase the resistanceof the protective reinforcement of an aircraft tire to piercing andcutting by foreign objects that have passed through the tread of thetire, namely to improve the resistance of the protective reinforcementto foreign object damage.

This objective is achieved by an aircraft tire comprising:

-   -   a tread, intended to come into contact with a ground,    -   a protective reinforcement, radially on the inside of the tread,    -   the protective reinforcement having a cylindrical structure        having as its axis of revolution the axis of rotation of the        tire, extending axially from a first axial end as far as a        second axial end over an axial width L and extending radially        from a radially interior first face as far as a radially        exterior second face over a mean radial thickness T,    -   the protective reinforcement comprising reinforcers coated in an        elastomer compound, having a diameter D and having a path in the        circumferential direction of the tire,    -   the protective reinforcement being radially on the outside of a        working reinforcement,    -   the working reinforcement comprising at least two radially        superposed working layers made up of reinforcers having a zigzag        path in the circumferential direction of the tire,    -   the protective reinforcement having a mean radial thickness T at        least equal to two times the diameter D of a reinforcer,    -   the protective reinforcement comprising respectively on its        radially interior face and on its radially exterior face parts        made of elastomeric compound having an axial width W at least        equal to the diameter D of a reinforcer,    -   the path of any reinforcer of the protective reinforcement, in        the circumferential direction of the tire, varies radially        between the radially interior first face and the radially        exterior second face, in such a way that the set of paths of the        reinforcers of the protective reinforcement constitutes a        three-dimensional lattice,    -   the path of any reinforcer of the protective reinforcement, in        the circumferential direction of the tire, is a zigzag curve        extending axially over the entire axial width L of the        protective reinforcement.

The principle of the invention is that of obtaining a protectivereinforcement that has both better mechanical connection at itsrespectively radially interior and exterior faces to the workingreinforcement and to the tread, and better resistance to unravelling ofthe reinforcers of which it is formed in the event of damage to the saidprotective reinforcement, thanks to the three-dimensional lattice workeffect, namely thanks to the effect whereby the reinforcers areinterlaced.

According to the invention, the mean radial thickness T of theprotective reinforcement is at least equal to two times the diameter Dof a reinforcer so as to be able to obtain the three-dimensional latticeeffect.

Again according to the invention, the protective reinforcement comprisesrespectively on its radially interior face and on its radially exteriorface parts made of elastomeric compound having an axial width W at leastequal to the diameter D of a reinforcer. In other words, at the radiallyinterior and, respectively, radially exterior, face there are parts madeof elastomeric compound without any reinforcer. In practice, duringmanufacture, prior to the tire-curing stage, these parts made ofelastomeric compound correspond to interstitial holes between thereinforcers which are then filled with an elastomeric compound at thetime of curing of the tire. Thus, on the radially interior and,respectively, exterior face, there is an alternation of parts comprisingreinforcers and of parts without reinforcers, the latter partscontributing to more effective connection to the components at theinterface with the protective reinforcement, such as the workingreinforcement and the tread. In order to be effective, these parts madeof elastomeric compound need to have a minimal dimension characterizedby a minimal axial width W equal to a reinforcer diameter D.

Another essential feature of the invention is that the path of anyreinforcer of the protective reinforcement, in the circumferentialdirection of the tire, varies radially between the radially interiorfirst face and the radially exterior second face, in such a way that theset of paths of the reinforcers of the protective reinforcementconstitutes a three-dimensional lattice. In other words, the path of anyreinforcer, in the circumferential direction, is not contained in acylindrical surface having as its axis of revolution the axis ofrotation of the tire. In addition, this path may or may not be variablein the axial direction. The result of this is that, in thecircumferential direction, any reinforcer is alternately radially on theoutside and radially on the inside of at least one other reinforcer. Theset of such reinforcers thus constitutes a cylindrical structure having,in its radial thickness, the form of a three-dimensional lattice orinterlacing, so that any reinforcer accidentally severed at some pointby a foreign object is immobilized by the other reinforcers in contactwith it and cannot unravel over the entire circumference. Thisthree-dimensional lattice is therefore a self-locking system thatguarantees that the reinforcers cannot become fully circumferentiallyunravelled.

A final essential feature of the invention is that of having a path ofany reinforcer of the protective reinforcement, in the circumferentialdirection of the tire, following a zigzag curve extending axially overthe entire axial width L of the protective reinforcement. From thestandpoint of the method of manufacturing such a protectivereinforcement, the reinforcers are usually laid in groups of reinforcersor strips using a method referred to as a reel-winding method. Thisreel-winding method, which consists in winding strips, in thecircumferential direction of the tire, on a periodic zigzag curve iscommonly used for laying the working layers of the working reinforcementof an aircraft tire. In the context of the invention, this reel-windingmethod is therefore also used for the protective reinforcement. Oneessential parameter is the period P of the periodic zigzag curve becauseit makes it possible to regulate the angle formed by the reinforcerswith the circumferential direction of the tire. Such a protectivereinforcement offers the advantage of being able to be manufacturedusing a conventional reel-winding method.

Advantageously, the protective reinforcement has a mean radial thicknessT at most equal to five times the diameter D of a reinforcer. Upwards ofthis maximum mean radial thickness T the protection is excessive and themass of the protective reinforcement becomes too great.

Advantageously again, the axial width W of the parts made of elastomericcompound, comprised respectively on the radially interior face and onthe radially exterior face of the protective reinforcement, is at mostequal to ten times the diameter D of a reinforcer, preferably at mostequal to five times the diameter D of a reinforcer. Upwards of thismaximum axial width W there is a risk that the protection will becomeless effective against the migration of foreign objects through theprotective reinforcement.

In any meridian plane, the ratio R, between the sum of the axial widthsW of the parts made of elastomeric compound, comprised respectively onthe radially interior face and on the radially exterior face of theprotective reinforcement, and the axial width L of the protectivereinforcement, is at least equal to 0.08, preferably at least equal to0.10. This ratio characterizes the percentage of reinforcer-free partswith respect to the axial width L of the protective reinforcement. Thisratio needs to have a minimal value in order to guarantee sufficientmechanical connection of the protective reinforcement on the one hand tothe working reinforcement and on the other hand to the tread.

In any meridian plane, the ratio R, between the sum of the axial widthsW of the parts made of elastomeric compound, comprised respectively onthe radially interior face and on the radially exterior face of theprotective reinforcement, and the axial width L of the protectivereinforcement, is at most equal to 0.20, preferably at most equal to0.15. This ratio needs to be kept at a maximum in order to guaranteethat the mechanical connection of the protective reinforcement to theworking reinforcement on the one hand and to the tread on the other isnot excessively strong.

According to a preferred embodiment, the reinforcers of the protectivereinforcement are grouped into strips, comprising at least twoconsecutive reinforcers. The use of strips of reinforcers comprising,for example and nonexhaustively, at least four reinforcers iscommonplace in the field of aircraft tires in order to obtainsatisfactory manufacturing productivity.

In the case of a protective reinforcement made up of strips, the axialspacing P1 between two consecutive strips of reinforcers each having apath, in the circumferential direction of the tire, that follows azigzag curve is at least equal to 0.5 times the axial width B of a stripand at most equal to five times the axial width B of a strip. The axialspacing between two consecutive strips is the name given to the axialdistance between their respective opposing axial ends. This spacingneeds to be large enough to guarantee that there will be interstitialspaces of elastomeric compound, but not too great, so as not to allowforeign objects to migrate radially towards the inside of the tire.

Advantageously, the path of any reinforcer, in the circumferentialdirection of the tire, is a periodic zigzag curve having an amplitude Aequal to the axial width L of the protective reinforcement and having aperiod P=2πR1/K, K being a non-integer number in the range ]N, N+1[where N is an integer at least equal to 0 and at most equal to 9,preferably at most equal to 4, and R1 being the radius of the radiallyinterior first face. Having the amplitude A equal to the axial width Lof the protective reinforcement allows the protective reinforcement tobe generated in a single hit across its entire width. The period P makesit possible to regulate the angle formed by the said reinforcers withthe circumferential direction, typically between 5° and 35°. The factthat K is a non-integer number, namely that the period P is not aninteger divisor of the developed placing surface 2πR1, guarantees thatbits of elastomer compound will be present respectively on the radiallyinterior face and on the radially exterior face of the protectivereinforcement.

According to a preferred alternative form, the reinforcers of theprotective reinforcement are made of at least one textile material. Thisis because a textile material guarantees a good compromise between themass and the breaking strength of the reinforcers. The use of textilereinforcers for the protective reinforcement makes a significantcontribution to minimizing the mass of the tire, and therefore improvingthe payload of the aircraft.

The reinforcers of the protective reinforcement are usually made of analiphatic polyamide or of an aromatic polyamide or of a combination ofan aliphatic polyamide and of an aromatic polyamide. Reinforcers made ofaromatic polyamide, such as aramid, offer a better compromise betweenmass and breaking strength than reinforcers made of aliphatic polyamide,such as nylon. Reinforcers made of a combination of an aliphaticpolyamide and of an aromatic polyamide, also referred to as hybridreinforcers, offer both the advantages of an aliphatic polyamide andthose of an aromatic polyamide, namely high breaking strength, hightensile strain and low mass.

The features and other advantages of the invention will be betterunderstood with the aid of the following FIGS. 1 to 4 which have notbeen drawn to scale:

FIG. 1: a half-view in cross section of the crown of an aircraft tire ofthe prior art, in a radial plane (YZ) passing through the axis ofrotation (YY′) of the tire.

FIG. 2: a meridian section through the protective reinforcement of anaircraft tire according to the invention, in a radial plane (YZ) passingthrough the axis of rotation (YY′) of the tire.

FIG. 3: a view from above of a circumferential portion of the protectivereinforcement of an aircraft tire according to the invention.

FIG. 4: a view from above of a protective reinforcement of an aircrafttire according to the invention, in the process of being manufactured.

FIG. 1 depicts, in a radial plane YZ passing through the axis ofrotation YY′ of the tire, a half-view in cross section of the crown ofan aircraft tire 1 of the prior art, comprising a tread 2 intended tocome into contact with a ground and a protective reinforcement 3,radially on the inside of the tread 2. The protective reinforcement 3 isa cylindrical structure having as its axis of revolution the axis ofrotation YY′ of the tire, extending axially from a first axial end E1 asfar as a second axial end E2, symmetric with respect to the equatorialplane XZ (not depicted) over an axial width L and extending radiallyfrom a radially interior first face 31 as far as a radially exteriorsecond face 32 over a mean radial thickness T. The protectivereinforcement 3 comprises reinforcers 4 coated in an elastomericcompound, having a diameter D and having a path in the circumferentialdirection XX′ of the tire. The protective reinforcement 3 is radially onthe outside of a working reinforcement 5 which in this instancecomprises four working layers that are radially superposed and made upof reinforcers 6 following a zigzag path in the circumferentialdirection XX′ of the tire (not depicted).

FIG. 2 depicts a meridian section of the protective reinforcement of anaircraft tire according to the invention, in a radial plane YZ passingthrough the axis of rotation YY′ of the tire. The protectivereinforcement 3 has a mean radial thickness T at least equal to twotimes the diameter D of a reinforcer 4, in this instance equal toapproximately five times the diameter D of a reinforcer 4. Theprotective reinforcement 3 respectively comprises, on its radiallyinterior face 31 and on its radially exterior face 32, parts 7 made ofelastomeric compound having an axial width W at least equal to thediameter D of a reinforcer 4. This meridian section also shows that thecollection of the paths of the reinforcers 4 of the protectivereinforcement 3 forms a three-dimensional lattice, resulting from thefact that the path of any reinforcer 4 of the protective reinforcement3, in the circumferential direction XX′ of the tire, varies radiallybetween the radially interior first face 31 and the radially exteriorsecond face 32. Furthermore, the reinforcers 4 of the protectivereinforcement 3 are grouped together in strips 8 comprising, in thisinstance, four consecutive reinforcers 4 and having an axial width B.

FIG. 3 depicts a view from above of a circumferential portion of theprotective reinforcement of an aircraft tire according to the invention.The protective reinforcement 3 depicted is made up of athree-dimensional lattice of strips of reinforcers extending, in thecircumferential direction XX′ of the tire, in a zigzag curve. FIG. 3more particularly shows the bits of elastomer compound 7, free of anyreinforcer and having an axial width W, the said bits guaranteeing astrong mechanical bond between the protective reinforcement 3 and thetread and the working reinforcement respectively.

FIG. 4 depicts a view from above of a protective reinforcement of anaircraft tire according to the invention, during the course ofmanufacture. The protective reinforcement 3 is manufactured according toa reel-winding method which consists in continuously winding, in thecircumferential direction (XX′) of the tire, a strip 8 made up ofreinforcers in a periodic zigzag curve. The periodic curve has anamplitude A equal to the axial width L of the protective reinforcement 3and a period P=2πR1/K, K being a non-integer number in the range ]N,N+1[ where N is an integer at least equal to 0 and at most equal to 9,preferably at most equal to 4, and R1 being the radius of the radiallyinterior first face 31. The strips 8 of width B are spaced apart by apitch P1. They form with the circumferential direction XX′ of the tirean angle D. FIG. 4 depicts the periodic paths corresponding respectivelyto 4 successive winding turns N, N+1, N+2 and N +3.

The inventors carried out the invention for an aircraft tire of size46×17 R 20 the protective reinforcement of which was a three-dimensionallattice obtained by a method of laying the protective reinforcement byreel-winding with an axial width L equal to 200 mm and a mean radialthickness T equal to 4 mm. The textile reinforcers of which theprotective reinforcement is made are made of nylon and have a diameter Dequal to 1 mm. The axial width W of the parts made of elastomericcompound is comprised between 2 mm and 7 mm.

1. Aircraft tire comprising: a tread, configured to come into contactwith a ground; a protective reinforcement, radially on the inside of thetread; the protective reinforcement having a cylindrical structurehaving as its axis of revolution the axis of rotation of the tire,extending axially from a first axial end as far as a second axial endover an axial width L and extending radially from a radially interiorfirst face as far as a radially exterior second face over a mean radialthickness T; the protective reinforcement comprising reinforcers coatedin an elastomer compound, having a diameter D and having a path in thecircumferential direction of the tire; the protective reinforcementbeing radially on the outside of a working reinforcement; the workingreinforcement comprising at least two radially superposed working layersmade up of reinforcers having a zigzag path in the circumferentialdirection of the tire; wherein the protective reinforcement has a meanradial thickness T at least equal to two times the diameter D of a saidreinforcer, wherein the protective reinforcement comprises respectivelyon its radially interior face and on its radially exterior face partsmade of elastomeric compound having an axial width W at least equal tothe diameter D of a said reinforcer, wherein the path of any saidreinforcer of the protective reinforcement, in the circumferentialdirection of the tire, varies radially between the radially interiorfirst face and the radially exterior second face, in such a way that theset of paths of said reinforcers of the protective reinforcementconstitutes a three-dimensional lattice and wherein the path of any saidreinforcer of the protective reinforcement, in the circumferentialdirection of the tire, is a zigzag curve extending axially over theentire axial width L of the protective reinforcement.
 2. The aircrafttire according to claim 1, wherein the protective reinforcement has amean radial thickness T at most equal to five times the diameter D of asaid reinforcer.
 3. The aircraft tire according to claim 1, wherein theaxial width W of the parts made of elastomeric compound, comprisedrespectively on the radially interior face and on the radially exteriorface of the protective reinforcement, is at most equal to ten times thediameter D of a said reinforcer.
 4. The aircraft tire according to claim1, wherein in any meridian plane, the ratio R, between the sum of theaxial widths W of the parts made of elastomeric compound, comprisedrespectively on the radially interior face and on the radially exteriorface of the protective reinforcement, and the axial width L of theprotective reinforcement, is at least equal to 0.08.
 5. The aircrafttire according to claim 1, wherein in any meridian plane, the ratio R,between the sum of the axial widths W of the parts made of elastomericcompound, comprised respectively on the radially interior face and onthe radially exterior face of the protective reinforcement, and theaxial width L of the protective reinforcement, is at most equal to 0.20.6. The aircraft tire according to claim 1, wherein the reinforcers ofthe protective reinforcement are grouped into strips, comprising atleast two consecutive reinforcers and having an axial width B.
 7. Theaircraft tire according to claim 6, wherein the axial spacing P1 betweentwo consecutive said strips of said reinforcers each having a path, inthe circumferential direction of the tire, that follows a zigzag curveis at least equal to 0.5 times the axial width B of a said strip and atmost equal to five times the axial width B of a said strip.
 8. Theaircraft tire according to claim 1, wherein the path of any saidreinforcer, in the circumferential direction of the tire, is a periodiczigzag curve having an amplitude A equal to the axial width L of theprotective reinforcement and having a period P=2□R1/K, K being anon-integer number in the range ]N, N+1[ where N is an integer at leastequal to 0 and at most equal to 9, and R1 being the radius of theradially interior first face.
 9. The aircraft tire according to claim 1,wherein the reinforcers of the protective reinforcement are made of atleast one textile material.
 10. The aircraft tire according to claim 1,wherein the reinforcers of the protective reinforcement are made of analiphatic polyamide or of an aromatic polyamide or of a combination ofan aliphatic polyamide and of an aromatic polyamide.
 11. The aircrafttire according to claim 1, wherein the axial width W of the parts madeof elastomeric compound, comprised respectively on the radially interiorface and on the radially exterior face of the protective reinforcement,is at most equal to five times the diameter D of a said reinforcer. 12.The aircraft tire according to claim 1, wherein, in any meridian plane,the ratio R, between the sum of the axial widths W of the parts made ofelastomeric compound, comprised respectively on the radially interiorface and on the radially exterior face of the protective reinforcement,and the axial width L of the protective reinforcement, is at least equalto 0.10.
 13. The aircraft tire according to claim 1, wherein, in anymeridian plane, the ratio R, between the sum of the axial widths W ofthe parts made of elastomeric compound, comprised respectively on theradially interior face and on the radially exterior face of theprotective reinforcement, and the axial width L of the protectivereinforcement, is at most equal to 0.15.
 14. The aircraft tire accordingto claim 1, wherein the path of any said reinforcer, in thecircumferential direction of the tire, is a periodic zigzag curve havingan amplitude A equal to the axial width L of the protectivereinforcement and having a period P=2□R1/K, K being a non-integer numberin the range ]N, N+1[ where N is an integer at least equal to 0 and atmost equal to 4, and R1 being the radius of the radially interior firstface.